Question

In a test, Rashi has to write the chemical equation for the formation of hydrochloric acid. She wrote

$H_2+2Cl\to 2HCl$

The teacher marked the answer wrong. Why is it so?

• A. The equation is not balanced.
• B. Hydrogen and chlorine do not react to form hydrochloric acid.
• C. In this 2 atoms of chlorine were used insteadof1 molecule of chlorine.
• D. In this 2 molecule of chlorine was used instead of 2 atoms of chlorine.

Answer 1

The correct option is C

In this 2 atoms of chlorine were used insteadof1 molecule of chlorine.

When we write the chemical equation we express the elements as they exist in their native or elemental form. This is because they react with other elements or compounds in this form only. In nature, both hydrogen and chlorine are diatomic and are expressed as $H_2$ and $C{l}_2$. Writing them as $H$ or $Cl$ is entirely wrong.

Hence, the correct equation should be:
$H_2+C{l}_2\to 2HCl$

Moreover, $2Cl$ means 2 atoms of chlorine while $C{l}_2$ means 1 molecule of chlorine consisting of 2 chlorine atoms.